The overall goal of this grant is to seek molecular therapies for diseases resulting from defects of the mitochondrial oxidative phosphorylation system. Complex I is the first of five enzyme complexes that comprise the oxidative phosphorylation system. It has the most intricate structure with 45 different subunits (of these, 7 subunits are mitochondrially encoded (designated ND1-6 and 4L)), one FMN and eight iron- sulfur clusters as cofactors. Complex I defects are involved in many human mitochondrial diseases. Leber's hereditary optic neuropathy (LHON) is recognized as the frequently occurring complex I disease. A new animal model has been developed that involves infusion of rotenone-biobeads into the superior colliculus of the rat brain. Symptoms typical of LHON were observed in the animals, most notably, severely impaired vision. At the same time, there was clearly disorganization of the node of Ranvier as well as demyelination of the RGC axons. However, loss of vision was not accompanied by the hallmarks of LHON such as thinner retinal ganglion cell (RGC) layer and death of RGC which only occurred at a later stage. Furthermore, delivery of the yeast alternative NADH dehydrogenase gene (NDI1) into the rat brain restored the vision to normal level with concomitant reorganization of the node of Ranvier and remyelination of the RGC axons. These findings form the basis of this research project. During this grant term, focus will be made on LHON research with the following specific aims. (i) To investigate mechanism of LHON by using the rat models by administration of mutated human or rat ND4 gene to the retina or rotenone biobeads infusion in the superior colliculus. (ii) To clarify whether the NDI1 gene expression can repair vision loss of the two LHON models and to determine repair window. (iii) To construct transgenic mouse strains carrying the mutated human or mouse ND4 gene for further investigation of LHON such as triggering factors.